1. Field of the Invention
The present invention relates generally to ultra-low-frequency communication systems. More particularly, the present invention relates to a portable wireless through-the-earth bi-directional communication system for providing wireless communication between people physically separated by the earth or other material that prevents the ability to communicate by traditional open-air communication systems. The present invention eliminates the need for current loop antennae, magnetic flux coupling, or leaky feeder cabling to communicate through the earth. The present system employs ultra-low-frequency electric fields to penetrate the earth thereby transmit longer distances, and establishes a wireless bi-directional communication system used for sending and receiving text messages or predefined data encoded beacons.
2. Description of the Related Art
There exists in the prior art through-the-earth communication systems which employ electromagnetic waves and loop antennas for transmitting and receiving audio and digital data between the surface and subsurface components. However, such systems are characterized as having limited through-the-earth range. Moreover, such systems require coupling of the magnetic field between the antennas. Proper alignment of the surface and subsurface loop antennas is required to achieve maximum transmission distance. To increase transmission distance in these systems, larger loop antennas may be employed, such as wrapping a wire around a coal pillar inside a coal mine.
However, these modifications are impractical and perhaps impossible in underground emergencies such as cave-ins or explosions. Increasing the transmission distance by increasing current flow through the loop is usually not available because energy transmission must be limited in most underground environments for safety purposes, as a spark ignition of explosive gases is possible. Thus, these systems result in providing much shorter transmission distances through the earth than is desirable to communicate with trapped personnel to aid in their rescue.
There also exists in the prior art wireless communication systems in mines using “leaky feeders” as radiating transmission lines. However, these systems require radiating transmission lines to be in place within the mines or underground areas, and to survive explosions and/or cave-ins in order to work, which is often not the case in many underground emergency situations. Thus, the leaky feeder systems are not reliable to be operational in underground emergency situations.